Method and apparatus for bending glass sheets

ABSTRACT

A method and apparatus for bending glass sheets in which a sheet is heated, prebent convexly upward by applying a jet of cool air to the upper surface thereof, and then bent in the opposite direction on an inertia-gravity bending mold. The apparatus includes an air nozzle which is arranged and controlled such that cooling air is applied only to the central area of the sheet in order to prevent edge vents from occurring.

United States Patent Inventor George F. Ritter, Jr.

Toledo, Ohio Appl. No. 861,000

Filed Sept. 25, 1969 Patented Jan. 4, i972 Assignee Libbey-Owens-FordCompany Toledo, Ohio METHOD AND APPARATUS FOR BENDING GLASS SHEETS 8Claims, 3 Drawing Figs.

Int. Cl C03b 23/02 Field of Search 65/104,

[56) References Cited UNITED STATES PATENTS 3,468,645 9/ i969 McMasteret al 65/l [4 X Primary Examiner-Arthur D. Kellogg Attorney-Collins andOberlin ABSTRACT: A method and apparatus for bending glass sheets inwhich a sheet is heated, prebent convexly upward by applying a jet ofcool air to the upper surface thereof, and then bent in the oppositedirection on an inertia-gravity bending mold. The apparatus includes anair nozzle which is arranged and controlled such that cooling air isapplied only to the central area of the sheet in order to prevent edgevents from occurring.

METHOD AND APPARATUS FOR BENDING GLASS SHEETS The present inventionrelates to the production of curved glass sheets and more particularlyto an improved method and apparatus for bending relatively large glasssheets by the inertiagravity method.

Curved sheets of glass are widely used as glazing closures for vehicles,such as automobiles or the like. To be suitable for such application thecurved sheets must be bent to precisely defined curvatures as dictatedby the overall styling of the vehicle and by the manner of mounting thesheet in its opening. At the same time, it is important that the sheetsmeet rather stringent optical requirements and more particularly thatthe viewing area of the window or light be free of optical defects whichwould tend to interfere with the clear viewing of an object through thewindow.

In general, the commercial production of curved glass sheets of theabove character includes heating the sheets to the softening point ofthe glass, bending the heated sheets to the desired curvature andthereafter subjecting them to a heattreating process such as annealingor tempering.

One particularly successful procedure for producing such bent sheets isthe socalled inertiagravity process, which is described in detail inU.S. Pat. application Ser. No. 573,969, filed in the names of George F.Ritter, Jr., Frank J. Carson and Frank J. Hymore, now US. Pat. No.3,476,540. According to this process the heatsoftened sheets arepositioned over a bending mold member and the mold and sheet are thenaccelerated rapidly in the direction opposite the desired direction ofbending whereby an inertial force is exerted against the sheet to forceit into registry with the shaping surface of the mold. Where the bendingmold is oriented horizontally, gravity forces also enter into thebending of the sheet.

The simplicity and speed of the inertiagravity process make itparticularly attractive for the production of automotive glass and acontinuing effort is being made to expand its use to larger sheets andmore complex and severe curvatures. One particular problem which ariseswhen attempting to bend sheets of the size currently required forautomobile sidelights and backlights, for example a 40 inch X 50 inchsheet with a 126 inch cylindrical bend, is that of cross bending. Theterm cross bending refers to the tendency for the sheet to bend about anaxis perpendicular to the desired axis of curvature which, if severeenough, can cause the sheet to be off form and not acceptable forproduction. While a certain amount of cross bending is allowable, itmust be held to reasonable limits.

Cross bending is most pronounced in sheets which are more nearly squareand begins when a heatsoftened sheet first comes into contact with themold, when the sheet is suspended between the ends of the mold and tendsto sag toward the mold. If the bent axis is relatively long it will saginto a catenary curve until the mold accelerates it into conformity withthe shaping surface thereof; however, if the sheet is more nearlysquare, it will tend to sag downward from the unsupported edges as well,resulting in a cross bend which may not be corrected after the mold isaccelerated, the edges perpendicular to the desired axis of curvatureremaining curled upward away from the mold. This is a most severeproblem in inertiagravity bending since there is no upper mold member tohelp force these edges into conformity with the shaping surface.

While attempts have been made to correct this by using auxiliary moldsections which contact only the edges which are intended to remainstraight, the use of additional mold members tends to detract from theadvantages of the inertiagravity method.

Accordingly, the primary object of the present invention is to producelarge, cylindrically bent sheets with a minimum of cross bending.

Another object of the invention is to produce such sheets by theinertiagravity method.

Another object of the invention is to produce such sheets without theuse of auxiliary mold members.

To accomplish these objectives, the present invention proposes toprebend or prebow the sheets, in a direction opposite that in which theyare ultimately bent, before they contact the mold member. As a result ofthis prebending, the initial sag of the sheet as it contacts the moldwill tend to return it to a flat condition at the time when the mold isaccelerated to force the sheet into registry with the shaping surface.Experience has shown that with an optimum degree of prebending, crossbending can be eliminated, or at least minimized.

To accomplish the desired prebending, the invention contemplatesapplying differential cooling to the sheet before bending, with thehigher degree of cooling being applied to the top of the sheets. This isknown to cause the sheet to bow upward at the center, opposite thedirection in which it will be bent.

Other objects and advantages of the invention will become more apparentduring the course of the following description when taken in connectionwith the accompanying drawings.

In the drawings, wherein like numerals are employed to designate likeparts throughout the same:

FIG. 1 is a side elevation view of a bending apparatus constructed inaccordance with the present invention;

FIG. 2 is a section view taken at line 2-2 of FIG. 1; and

FIG. 3 is an enlarged elevation view, with parts cut away, of thecooling means in the prebending section.

Referring to the drawings, there is illustrated a glass bendingapparatus in which sheets of glass are transferred along a horizontalpath through a heating section A where they are heated to the softeningpoint, a prebending section B where they are initially bowed upward atthe center, and a bending section C where the sheets are bent in theopposite direction into conformity with a bending mold.

Referring particularly to FIG. 1, the bending section consistsessentially of a movable mold member 11 and an actuator 12 capable ofaccelerating the mold member rapidly upward, both suitably mountedwithin a rigid framework 13, and operating in conjunction with aconveyor system comprising entry and prebending rolls l4, bendingsection rolls l5, and exit rolls 16, all mounted on rail sections 17running along either side of the framework 13.

The bending mold member 11 comprises an outline or ringtype shapingelement 18 having a contoured shaping surface 19 formed on its upperface which engages only the marginal edge portions of a sheet 20 to bebent. The shaping element 18 is supported by a plurality of verticalbars 21 upstanding from a horizontal base member 22. Since the moldmember 11 is vertically movable to lift a sheet 20 from the rolls 15,the shaping element 18 is made up of a plurality of sections includingtransverse end sections 23 and longitudinal side sections 24, spacedapart to provide clearance for the rolls.

The base member 22 is fastened to a carriage 25, and the carriage issupported by telescoping guide members 26 which allow vertical movementonly, said vertical movement being provided by the ram 27 of a pressurecylinder 28 which bears against the bottom of the carriage.

When a sheet 20 is conveyed into position to be bent above the moldmember 11 it is halted by engagement of its leading edge with locatorstops 29 (one of two shown) which are moved into and out of the path ofsheet movement by pressure cylinders 30 mounted on the base member 22.When the sheet 20 contacts the stops fluid pressure is applied to thelower end of cylinder 28 to rapidly move the mold member 11 upwardlifting the sheet from the conveyor rolls 15. As the sheet isaccelerated rapidly upward, combined inertial and gravitational forcescause to to sag into conformity with the mold. Once the sheet is liftedfree of the rolls the stops 29 are returned to their normal positionbelow the conveyor.

The prebending section comprises one or more air nozzles 31 mounted inposition to direct cooling air against the tops of sheets traveling onthe conveyor rolls 14, the air nozzle(s) including a regulating valve 32which controls the flow of air therethrough. For purposes ofillustration, a single nozzle is shown suspended from a crossmember 33extending between vertical columns 34, one of which can be part of theframework 13. The nozzle 31 comprises an elongated tapered hood 35,enclosed by inclined walls 37 terminating in an elongated slot 38, endwalls, and a channel section 39 which forms a top wall; a supply tube 40connected to the top wall and extending upward therefrom; and a tubularvalve body 41 which encloses the valve 32 and connects the supply tube40 to a source of pressurized air through a flexible conduit 42 andfitting 43. Vertical angle members 44 connect the channel member 39 to asimilar channel member 45 which is bolted or otherwise fastened to thecrossmember 33 to mount the nozzle. The valve 32, comprises the body 41,a clapper or butterfly element 46 capable of closing off the passagewaythrough the tube, and an actuator 47 adapted to rotate the butterflyelement 46 by means of a pivot arm 48. in the illustrative embodiment,the actuator comprises a pressure cylinder 49 pivotally suspended fromthe channel member 45 and having a ram 50. linked to the pivot arm 48.

Since there is a tendency for edge vents to form when differentialcooling is applied to sheets coming directly from the furnace, thenozzle 31 is arranged and controlled so that only a central area boundedapproximately by the dashed line a in FIG. 2, is subjected to thecooling air. In the transverse direction this is accomplished simply bysetting the length of the hood 35 accordingly; however, in thelongitudinal direction this must be accomplished by controlling theairflow since the sheet moves along the conveyor. Although there areseveral wellknown methods of performing such a control function, in theillustrative embodiment a photocell comprising a light source 52 andreceiver 53 are positioned to detect the arrival of a sheet 20 at somepredetermined point. By connecting the photocell in a circuit withwellknown timing devices such as time delay relays and to a solenoidvalve controlling airflow through the valve 32, the air nozzle can becontrolled so that air is applied just after the leading edge of thesheet passes the opening 38 of the hood 35 and is shut off just beforethe trailing edge passes.

OPERATION As a heatsoftened sheet 20 leaves the heating section A it iscarried beneath the air nozzle 31 which applies a relatively smallamount of cooling air to the area bounded by the line a (FIG. 2),causing the center of the sheet to bow upward. Although this wouldappear to be contrary to normally understood theories of expansion andcontraction, what apparently happens is that as soon as the air hits theupper surface of the sheet it tends to set before any significantcontraction can take place. The lower surface has more time to contractbefore it starts to set, and its contraction causes the sheet to bowconvexly toward the surface which is more rapidly cooled. It can beappreciated that the degree of differential cooling will determine theextent of the bow.

As the sheet, which is still in a heatsoftened condition, enters thebending area C it will be in a bowed condition as depicted in FIG. 1 andsagging toward the mold. As soon as it contacts the stops 29 pressurizedfluid is applied to the bottom of cylinder 28 causing the mold member tobe raised, lifting the sheet 20 from the rolls and accelerating itrapidly upward to cause it to bend into conformity with the shapingsurface 19. It can be appreciated that for every different size sheetand for every curvature there will be some optimum degree of prebendingwhich will produce a sheet having a minimum cross bend.

I claim:

1. In a method for bending horizontally disposed heat-sottened glasssheets by accelerating a sheet upwardly to cause it to sag intoconformity with a concave shaping surface, the improvement comprisingthe step of prebending the sheet in the opposite direction from thedesired bend, before it is subjected to said acceleration, bydifferentially cooling the upper and lower surfaces of the sheet withthe greater cooling being applied to the upper surface.

2. A method for bending glass sheets as claimed in claim 1, in which atleast one surface of said sheet is cooled by sweepingwith pressurizedcooling as.

A method for bending glass sheets as claimed in claim 2, in which theupper surface only is swept by cooling gas.

4. A method for bending glass sheets as claimed in claim 2, in whichsaid pressurized gas is applied to the central area only of the sheetsurfaces, leaving the marginal edge portions substantially untouchedthereby.

5. A method for bending horizontally disposed glass sheets, comprisingthe steps of heating a sheet to the softening point, prebending thesheet by applying cooling air to the central area of the upward facingsurface thereof, supporting said sheet over a bending mold having acontoured, upwardfacing shaping surface formed thereon, and thenaccelerating said mold member rapidly upward to lift said sheet bodilyto cause it to sag in conformity with said shaping surface under theinfluence of inertial and gravitational forces.

6. A method of bending each of a plurality of glass sheets, comprisingsupporting each sheet in a substantially horizontal plane, moving thesheet thus supported along a predetermined path, heating the sheet as ittravels along said path to substantially the softening point of theglass, initially cooling the upper surface only of said sheet as itmoves along said path at a rate sufficient to cause the center of saidsheet to bow upward to a predetermined curvature, stopping said sheetabove a bending mold member having an upward facing concave shapingsurface formed thereon, moving said mold member upward through said pathinto contact with the sheet, and then accelerating said mold member andsaid sheet bodily upward, said acceleration being sufficient to causethe sheet to settle into registry with said shaping surface under theinfluence of inertial and gravitational forces.

7. in apparatus for bending each of a plurality of horizontally disposedglass sheets, including means for moving said sheets along a horizontalpath; a furnace disposed along said path for heating said sheets to thesoftening point; and bending means disposed along said path beyond saidfurnace, said bending means comprising a ringtype mold member having anupward-facing, concave shaping surface formed thereon disposed belowsaid path, and means for accelerating said mold member upwardly to liftsaid sheet bodily upward from said path thereby creating combinedinertial and gravitational forces bending said sheet into registry withsaid shaping surface; the improvement which comprises locatingprebending means, comprising means for cooling a portion of the uppersurface of a sheet to cause the sheet to bow upwardly at the center,above said sheet and between said furnace and said bending means.

8. Apparatus for bending glass sheets as claimed in claim 7, includingmeans for restricting the effective area of said cooling means to anarea spaced inwardly of the marginal edge portions of said sheet.

1. In a method for bending horizontally disposed heat-softened glasssheets by accelerating a sheet upwardly to cause it to sag intoconformity with a concave shaping surface, the improvement comprisingthe step of prebending the sheet in the opposite direction from thedesired bend, before it is subjected to said acceleration, bydifferentially cooling the upper and lower surfaces of the sheet withthe greater cooling being applied to the upper surface.
 2. A method forbending glass sheets as claimed in claim 1, in which at least onesurface of said sheet is cooled by sweeping with pressurized coolinggas.
 3. A method for bending glass sheets as claimed in claim 2, inwhich the upper surface only is swept by cooling gas.
 4. A method forbending glass sheets as claimed in claim 2, in which said pressurizedgas is applied to the central area only of the sheet surfaces, leavingthe marginal edge portions substantially untouched thereby.
 5. A methodfor bending horizontally disposed glass sheets, comprising the steps ofheating a sheet to the softening point, prebending the sheet by applyingcooling air to the central area of the upward facing surface thereof,supporting said sheet over a bending mold having a contoured,upward-facing shaping surface formed thereon, and then accelerating saidmold member rapidly upward to lift said sheet bodily to cause it to sagin conformity with said shaping surface under the influence of inertialand gravitational forces.
 6. A method of bending each of a plurality ofglass sheets, comprising supporting each sheet in a substantiallyhorizontal plane, moving the sheet thus supported along a predeterminedpath, heating the sheet as it travels along said path to substantiallythe softening point of the glass, initially cooling the upper surfaceonly of said sheet as it moves along said path at a rate sufficient tocause the center of said sheet to bow upward to a predeterminedcurvature, stopping said sheet above a bending mold member having anupward facing concave shaping surface formed thereon, moving said moldmember upward through said path into contact with the sheet, and thenaccelerating said mold member and said sheet bodily upward, saidacceleration being sufficient to cause the sheet to settle into registrywith said shaping surface under the influence of inertial andgravitational forces.
 7. In apparatus for bending each of a plurality ofhorizontally disposed glass sheets, including means for moving saidsheets along a horizontal path; a furnace disposed along said path forheating said sheets to the softening point; and bending means disposedalong said path beyond said furnace, said bending means comprising aring-type mold member having an upward-facing, concave shaping surfaceformed thereon disposed below said path, and means for accelerating saidmold member upwardly to lift said sheet bodily upward from said paththereby creating combined inertial and gravitational forces bending saidsheet into registry with said shaping surface; the improvement whichcomprises locating prebending means, comprising means for cooling aportion of the upper surface of a sHeet to cause the sheet to bowupwardly at the center, above said sheet and between said furnace andsaid bending means.
 8. Apparatus for bending glass sheets as claimed inclaim 7, including means for restricting the effective area of saidcooling means to an area spaced inwardly of the marginal edge portionsof said sheet.